With increasingly stricter air quality standards being imposed in various communities and with increasingly greater energy needs experienced, it has become necessary to utilize all available sources of energy. One of the most plentiful sources of energy is coal found in deposits in numerous locations. Although coal has been used for many purposes, it has been gradually displaced by employing oil as an alternative fuel, because oil can be more readily purified.
In general, the most objectionable aspect when using coal has been air quality criteria which must be met when coal is burned. The combustion effluents or gases of coal such as high sulfur coal are laden with sulfur dioxide, the removal of which becomes fairly complex at the high flow rates and flue gas temperatures encountered such as in normal coal power plant boilers. For purposes of the present invention a high sulfur coal is defined as coal having more than 0.5% by weight of sulfur present.
Still further, in operating reverberatory furnaces, such as in smelters, the waste gases from these furnaces contain considerable amounts of sulfur dioxide. Waste gases from these furnaces contain from 0.5 to 3.5% of sulfur dioxide, by volume. In general, the sulfur dioxide from these combustion sources might be removed by a lime or limestone reaction by various processes and apparatus, numerous disclosures of which exist in the patent art literature. However, in contacting the sulfur dioxide laden flue gases in a wet lime or limestone scrubber, scale formations and encrustation of the apparatus are observed which render the apparatus employed for scrubbing of the flue gas useless after a short duration, requiring frequent shutdowns or an alternate apparatus to which the flue gas stream can be switched while scale and encrustations are removed from the substantially inoperative apparatus.